Method and apparatus for performing cell management in wireless communication system

ABSTRACT

A method for and apparatus for performing a cell management in a wireless communication system is provided. A wireless device detects a cell configuration based on a cell state, the cell state is determined by at least one of a number of UEs, a data offloading, a traffic pattern, and a UE mobility. The cell state includes a dormant or a low_active in which a resource for the reference signal is smaller than a resource for a high_active, and a transmission period of the reference signal when the cell state is in the dormant or the low_active is longer than a transmission period of a reference signal when a cell state is in the high_active. Thus, a cell specific RSs such as CRS, SIB, or paging and synchronization transmission as overhead in a cell can be minimized and controlled based on the active UEs.

This application is a National Stage Entry of International ApplicationNo. PCT/KR2014/002186, filed Mar. 14, 2014, and claims the benefit ofpriority to U.S. Provisional Application No. 61/786,634, filed Mar. 15,2013, both of which are incorporated by reference in their entirety forall purposes as if fully set forth herein.

TECHNICAL FIELD

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for performing a cell managementin a wireless communication system consisting of multiple carriers oversingle frequency or multiple frequencies.

BACKGROUND ART

3rd generation partnership project (3GPP) long term evolution (LTE) isan improved version of a universal mobile telecommunication system(UMTS) and a 3GPP release 8. The 3GPP LTE uses orthogonal frequencydivision multiple access (OFDMA) in a downlink, and uses singlecarrier-frequency division multiple access (SC-FDMA) in an uplink. The3GPP LTE employs multiple input multiple output (MIMO) having up to fourantennas. In recent years, there is an ongoing discussion on 3GPPLTE-advanced (LTE-A) that is an evolution of the 3GPP LTE.

The commercialization of the 3GPP LTE (A) system is being recentlyaccelerated. The LTE systems are spread more quickly as respond tousers' demand for services that may support higher quality and highercapacity while ensuring mobility, as well as voice services. The LTEsystem provides for low transmission delay, high transmission rate andsystem capacity, and enhanced coverage.

To increase the capacity for the users' demand of services, increasingthe bandwidth may be essential, a carrier aggregation (CA) technologyaiming at obtaining an effect, as if a logically wider band is used, bygrouping a plurality of physically non-continuous bands in a frequencydomain has been developed to effectively use fragmented small bands.Individual unit carriers grouped by carrier aggregation is known as acomponent carrier (CC). Each CC is defined by a single bandwidth and acenter frequency.

A system in which data is transmitted and/or received in a broadbandthrough a plurality of CCs is referred to as a multi-component carriersystem (multi-CC system) or a CA environment. The multi-componentcarrier system performs both a narrow band and a broad band by using oneor more carriers. For example, when an each carrier corresponds to abandwidth of 20 MHz, a bandwidth of a maximum of 100 MHz may besupported by using five carriers.

In order to operate the multi-CC system, various control signals arerequired between a base station (BS) as an eNB (enhanced Node B) and aUser equipment as a Terminal. Also an efficient cell planning formulti-CCs is required. Also various signals or efficient cell planningschemes are required to transmit between the eNB and the UE to supportinter-cell interference reduction and carrier extensions. Furthermore,inter-node resource allocation by tight coordination among eNBs for a UEis also feasible where multi-CC aggregation is achieved over multipleeNBs/nodes. An efficient operation scheme for the cell planningincluding a new carrier which is necessarily transmitted restricted (oreliminated) controls and UE in a small cell cluster environment needs tobe defined. Furthermore, it needs to be defined a cell state change andmanagement to use limited resources for efficiency.

DISCLOSURE Technical Problem

The present invention provides a method and apparatus for performing acell management in a wireless communication system.

The present invention also provides a method and apparatus forperforming a cell state change in a wireless communication system.

The present invention also provides a method and apparatus fortransmitting a cell reference signal in a wireless communication system.

Technical Solution

In an aspect, a method for performing a cell management in a wirelesscommunication system is provided. The method may includes receiving aradio resource configuration based on a cell state; detecting areference signal via the cell; determining the cell state by thereference signal; and adapting a radio resource measurement based on acell state,

wherein the cell state includes a dormant or a low_active in which aresource for the reference signal is smaller than a resource for ahigh_active, and a transmission period of the reference signal when thecell state is in the dormant or the low_active is longer than atransmission period of a reference signal when a cell state is in thehigh_active.

In another aspect, an user equipment (UE) for performing a cellmanagement in a wireless communication system is provided. The UEincludes a radio frequency (RF) unit for transmitting and receiving aradio signal; and a processor operatively coupled to the RF unit,wherein the processor is configured for: receiving a radio resourceconfiguration based on a cell state; detecting a reference signal viathe cell; determining the cell state by the reference signal; andadapting a radio resource measurement based on a cell state,

wherein the cell state includes a dormant or a low_active in which aresource for the reference signal is smaller than a resource for ahigh_active, and a transmission period of the reference signal when thecell state is in the dormant or the low_active is longer than atransmission period of a reference signal when a cell state is in thehigh_active.

Advantageous Effects

The proposed embodiment supports a dynamic cell change of a small cellfor a user equipment so that the UE receives and detects referencesignals with more efficiency and optimized RS resource.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a wireless communication system to which the presentinvention is applied.

FIG. 2 shows an exemplary concept for a carrier aggregation (CA)technology according to an exemplary embodiment of the presentinvention.

FIG. 3 shows a structure of a radio frame to which the present inventionis applied.

FIG. 4 is an exemplary diagram showing a resource grid for one downlinkslot to which the present invention is applied.

FIG. 5 shows a structure of a downlink subframe to which the presentinvention is applied.

FIG. 6 shows an example of a structure of an uplink subframe carrying anACK/NACK signal to which the present invention is applied.

FIG. 7 shows downlink control channels to which the present invention isapplied.

FIG. 8 shows examples of ePDCCH monitoring subframe set which thepresent invention is applied.

FIG. 9 and FIG. 10 shows examples of dynamic cell configuration based ona cell state which the present invention is applied.

FIG. 11 shows a block diagram showing a wireless communication systemaccording to an exemplary embodiment of the present invention.

MODE FOR INVENTION

FIG. 1 shows a wireless communication system to which the presentinvention is applied. The wireless communication system may also bereferred to as an evolved-UMTS terrestrial radio access network(E-UTRAN) or a long term evolution (LTE)/LTE-A system.

The E-UTRAN includes at least one base station (BS) 20 which provides acontrol plane and a user plane to a user equipment (UE) 10. The UE 10may be fixed or mobile, and may be referred to as another terminology,such as a mobile station (MS), a user terminal (UT), a subscriberstation (SS), a mobile terminal (MT), a wireless device, etc. The BS 20is generally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as an evolved node-B (eNB), abase transceiver system (BTS), an access point, etc.

Multi-access schemes applied to the wireless communication system arenot limited. Namely, various multi-access schemes such as CDMA CodeDivision Multiple Access), TDMA (Time Division Multiple Access), FDMA(Frequency Division Multiple Access), OFDMA (Orthogonal FrequencyDivision Multiple Access), SC-FDMA (Single Carrier-FDMA), OFDM-FDMA,OFDM-TDMA, OFDM-CDMA, or the like, may be used. For uplink transmissionand downlink transmission, a TDD (Time Division Duplex) scheme in whichtransmission is made by using a different time or an FDD (FrequencyDivision Duplex) scheme in which transmission is made by using differentfrequencies may be used.

The BSs 20 are interconnected by means of an X2 interface. The BSs 20are also connected by means of an S1 interface to an evolved packet core(EPC) 30, more specifically, to a mobility management entity (MME)through S1-MME and to a serving gateway (S-GW) through S1-U.

The EPC 30 includes an MME, an S-GW, and a packet data network-gateway(P-GW). The MME has access information of the UE or capabilityinformation of the UE, and such information is generally used formobility management of the UE. The S-GW is a gateway having an E-UTRANas an end point. The P-GW is a gateway having a PDN as an end point.

Layers of a radio interface protocol between the UE and the network canbe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. Among them, a physical (PHY) layer belonging to the first layerprovides an information transfer service by using a physical channel,and a radio resource control (RRC) layer belonging to the third layerserves to control a radio resource between the UE and the network. Forthis, the RRC layer exchanges an RRC message between the UE and the BS.

FIG. 2 shows an exemplary concept for a carrier aggregation (CA)technology according to an exemplary embodiment of the presentinvention.

Referring to FIG. 2, the DL/UL subframe structure considered in 3GPPLTE-A (LTE-Advanced) system where multiple CCs are aggregated (in thisexample, 3 carriers exist) is illustrated, a UE can monitor and receiveDL signal/data from multiple DL CCs at the same time. However, even if acell is managing N DL CCs, the network may configure a UE with M DL CCs,where M≦N so that the UE's monitoring of the DL signal/data is limitedto those M DL CCs. In addition, the network may configure L DL CCs asthe main DL CCs from which the UE should monitor/receive DL signal/datawith a priority, either UE-specifically or cell-specifically, whereL≦M≦N. So the UE may support one or more carriers (Carrier 1 or moreCarriers 2 . . . N) according to UE's capability thereof.

Hereinafter, a CC may be divided into a primary component carrier (PCC)and a secondary component carrier (SCC) depending on whether or not theyare activated. A PCC is a carrier which is constantly activated, and anSCC is a carrier which is activated or deactivated according toparticular conditions. Here, activation refers to a state in whichtraffic data is transmitted or received or a state in which traffic datais ready to be transmitted or received. Deactivation refers to a statein which traffic data cannot be transmitted or received and measurementor transmission or reception of minimum information is available.Furthermore, the PCC can be also activated or deactivated using anindication of activation/Deactivation as a bit. The UE can camp on thePCC as a Primary serving cell (Pcell) at first in initial access. The UEmay use only one primary component carrier or one or more secondarycomponent carriers along with a primary component carrier. The UE may beallocated a primary component carrier and/or a secondary componentcarrier from the BS.

A PCC is a carrier by which primary control information items areexchanged between a BS and an UE. An SCC is a carrier allocatedaccording to a request from an UE or an instruction from a BS. A PCC maybe used for an UE to enter a network and/or may be used to allocate anSCC. A PCC may be selected from among entire set carriers, rather thanbeing fixed to a particular carrier. A carrier set as an SCC may also bechanged into a PCC.

As described above, a DL CC may construct one serving cell, and the DLCC and a UL CC may construct one serving cell by being linked with eachother. Further, a primary serving cell (PCell) corresponds to a PCC, anda secondary serving cell (SCell) corresponds to an SCC. Each carrier andcombination of carriers may also be referred to as each one serving cellas a PCell or a SCell. That is, the one serving cell may correspond toonly one DL CC, or may correspond to both the DL CC and the UL CC.

A Pcell is a resource in which the UE initially establishes a connection(or a RRC connection) among several cells. The Pcell serves as aconnection (or RRC connection) for signaling with respect to a pluralityof cells (CCs), and is a special CC for managing UE context which isconnection information related to the UE. Further, when the Pcell (PCC)establishes the connection with the UE and thus is in an RRC connectedmode, the PCC always exists in an activation state. A SCell (SCC) is aresource assigned to the UE other than the Pcell (PCC). The SCell is anextended carrier for additional resource assignment, etc., in additionto the PCC, and can be divided into an activation state and adeactivation state. The SCell is initially in the deactivation state. Ifthe SCell is deactivated, it includes not transmit SRS on the SCell, notreport CQI/PMI/RI/PTI for the SCell, not transmit on UL-SCH on theSCell, not monitor the PDCCH on the SCell, not monitor the PDCCH for theSCell. The UE receives an Activation/Deactivation MAC control element inthis TTI activating or deactivating the SCell.

A MAC control element including an activation indicator has a length of8 bits, is used for activation for each serving cell. Herein, a Pcell isimplicitly regarded as being activated between the UE and the eNB and,thus the Pcell is not additionally included in the activation indicator.An index of the Pcell is always given a specific value, and it isassumed herein that the index is given 0. So the Scells are indexed with1, 2, 3, . . . 7 for a serving cell index 1 corresponds to a 7^(th) bitfrom the left, which are the remaining indices other than 0, i.e., theindex of the Pcell.

To enhance the user throughput, it is also considered to allowinter-node resource aggregation over more than one eNB/node where a UEmay be configured with more than one carrier groups. In such cases, itis also feasible to configure PCell per each carrier group whichparticularly may not be deactivated. In other words, PCell per eachcarrier group may maintain its state to active all the time once it isconfigured to a UE. In that case, serving cell index i corresponding toa PCell in a carrier group which does not include serving cell index 0(which is master PCell) cannot be used for activation/deactivation. Moreparticularly, if serving cell index 0, 1, 2 are configured by onecarrier group whereas serving cell index 3, 4, 5 are configured by theother carrier group in two carrier group scenarios where serving cellindex 0 is PCell and serving cell index 3 is the PCell of the secondcarrier group, then only bits corresponding 1 and 2 are assumed to bevalid for the first carrier group cell activation/deactivation messageswhereas bits corresponding 4 and 5 are assumed to be valid for thesecond carrier group cell activation/deactivation.

To make some distinction between PCell for the first carrier group andthe second carrier group, the PCell for the second carrier group can benoted as a S-PCell hereinafter. Herein, the index of the serving cellmay be a logical index determined relatively for each UE, or may be aphysical index for indicating a cell of a specific frequency band. TheCA system supports a non-cross carrier scheduling (self-carrierscheduling), or cross carrier scheduling.

FIG. 3 shows a structure of a radio frame to which the present inventionis applied.

Referring to FIG. 3, a radio frame includes 10 subframes, and onesubframe includes two slots. The time taken for one subframe to betransmitted is called a Transmission Time Interval (TTI). For example,the length of one subframe may be 1 ms, and the length of one slot maybe 0.5 ms.

One slot includes a plurality of OFDM symbols in the time domain andincludes a plurality of Resource Blocks (RBs) in the frequency domain.An OFDM symbol is for representing one symbol period because downlinkOFDMA is used in 3GPP LTE system and it may be called an SC-FDMA symbolor a symbol period depending on a multi-access scheme. An RB is aresource allocation unit, and it includes a plurality of contiguoussubcarriers in one slot. The number of OFDM symbols included in one slotmay vary according to the configuration (configuration) of the CP(Cyclic Prefix).

The CP includes an extended CP and a normal CP. For example, if normalCP case, the OFDM symbol is composed by 7. If configured by the extendedCP, it includes 6 OFDM symbols in one slot. If the channel status isunstable such as moving at a fast pace UE, the extended CP can beconfigured to reduce an inter-symbol interference.

Herein, the structure of the radio frame is only illustrative, and thenumber of subframes included in a radio frame, or the number of slotsincluded in a subframe, and the number of OFDM symbols included in aslot may be changed in various ways to apply new communication system.This invention has no limitation to adapt to other system by varying thespecific feature and the embodiment of the invention can apply withechangeable manners to a corresponding system.

FIG. 4 is an exemplary diagram showing a resource grid for one downlinkslot to which the present invention is applied.

Referring to FIG. 4, the downlink slot includes a plurality of OFDMsymbols in the time domain. For example, one downlink slot isillustrated as including 7 OFDMA symbols and one Resource Block (RB) isillustrated as including 12 subcarriers in the frequency domain, but notlimited thereto.

Each element on the resource grid is called a Resource Element (RE). Oneresource block includes 12×7 (or 6) REs. The number N^(DL) of resourceblocks included in a downlink slot depends on a downlink transmissionbandwidth that is set in a cell. Bandwidths that are taken into accountin LTE are 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz. If thebandwidths are represented by the number of resource blocks, they are 6,15, 25, 50, 75, and 100, respectively. One or more resource blockscorresponding to each band may be combined to form a Resource BlockGroup (RBG). For example, two contiguous resource blocks may form oneresource block group.

In LTE, the total number of resource blocks for each bandwidth and thenumber of resource blocks that form one resource block group are shownin Table 1.

TABLE 1 Total Number of RBs Total number belonging to number Bandwidthof RBs one RBG of RBGs 1.4 MHz 6 1 6 3 MHz 15 2 8 5 MHz 25 2 13 10 MHz50 3 17 15 MHz 75 4 19 20 MHz 100 4 25

Referring to Table 1, the total number of available resource blocks isdifferent depending on a given bandwidth. What the total number ofresource blocks differs means that the size of information indicative ofresource allocation is different.

FIG. 5 shows a structure of a downlink subframe to which the presentinvention is applied.

Referring to FIG. 5, a subframe includes two slots. The former 0 or 1 or2 or 3 OFDM symbols of the first slot within the subframe correspond toa control region to be assigned with a control channel, and theremaining OFDM symbols thereof become a data region to which a physicaldownlink shared chancel (PDSCH) is allocated.

Examples of downlink control channels used in the 3GPP LTE include aPhysical Control Format Indicator Channel (PCFICH), a Physical DownlinkControl Channel (PDCCH), and a Physical Hybrid-ARQ Indicator Channel(PHICH).

The PCFICH transmitted in a 1st OFDM symbol of the subframe carries acontrol format indicator (CFI) regarding the number of OFDM symbols(i.e., a size of the control region) used for transmission of controlchannels in the subframe, that is, carries information regarding thenumber of OFDM symbols used for transmission of control channels withinthe subframe. The UE first receives the CFI on the PCFICH, andthereafter monitors the PDCCH.

The PHICH carries acknowledgement (ACK)/not-acknowledgement (NACK)signals in response to an uplink Hybrid Automatic Repeat Request (HARM).That is, ACK/NACK signals for uplink data that has been transmitted by aUE are transmitted on a PHICH.

A PDCCH (or ePDCCH) is a downlink physical channel, a PDCCH can carryinformation about the resource allocation and transmission format of aDownlink Shared Channel (DL-SCH), information about the resourceallocation of an Uplink Shared Channel (UL-SCH), paging informationabout a Paging Channel (PCH), system information on a DL-SCH,information about the resource allocation of a higher layer controlmessage, such as a random access response transmitted on a PDSCH, a setof transmit power control commands for UEs within a certain UE group,the activation of a Voice over Internet Protocol (VoIP), etc. Aplurality of PDCCHs may be transmitted within the control region, and aUE can monitor a plurality of PDCCHs. Here, the ePDCCH is shown in FIG.7 more details.

The PDCCH is transmitted on one Control Channel Element (CCE) or on anaggregation of some contiguous CCEs. A CCE is a logical assignment unitfor providing a coding rate according to the state of a radio channel toa PDCCH. The CCE corresponds to a plurality of resource element groups(REGs). A format of the PDCCH and the number of bits of the availablePDCCH are determined according to a correlation between the number ofCCEs and the coding rate provided by the CCEs. The BS determines a PDCCHformat according to a Downlink Control Information (DCI) to betransmitted to the UE, and attaches a cyclic redundancy check (CRC) tocontrol information. The DCI includes uplink or downlink schedulinginformation or includes an uplink transmit (Tx) power control commandfor arbitrary UE groups. The DCI is differently used depending on itsformat, and it also has a different field that is defined within theDCI. Table 2 shows DCIs according to a DCI format.

TABLE 2 DCI format Description 0 Used for the scheduling of a PUSCH(uplink grant) 1 Used for the scheduling of one PDSCH codeword 1A Usedfor the simplified scheduling of one PDSCH codeword and for a randomaccess procedure reset by a PDCCH command 1B Used for the simplifiedscheduling of one PDSCH codeword using precoding information 1C Used forthe simplified scheduling of one PDSCH codeword and the notification ofa change of an MCCH 1D Used for precoding and the simplified schedulingof one PDSCH codeword including power offset information 2 Used forPDSCH scheduling for a UE configured in spatial multiplexing mode 2AUsed for the PDSCH scheduling of a UE configured in large delay CDD mode2B Used for Resource assignments for PDSCH using up to 2 antenna portswith UE-specific reference signals 2C Used for Resource assignment forPDSCH using up to 8 antenna ports with UE-specific reference signals 2DUsed for Resource assignment for PDSCH using up to 8 antenna ports withUE-specific reference signals 3 Used for the transmission of a TPCcommand for a PUCCH and PUSCH including 2-bit power coordination 3A Usedfor the transmission of a TPC command for a PUCCH and PUSCH includingsingle bit power coordination

The DCI Format 0 ndicates uplink resource allocation information, theDCI formats 1˜2 indicate downlink resource allocation information, andthe DCI formats 3 and 3A indicate uplink Transmit Power Control (TPC)commands for specific UE groups. The fields of the DCI are sequentiallymapped to an information bit. For example, assuming that DCI is mappedto an information bit having a length of a total of 44 bits, a resourceallocation field may be mapped to a 10^(th) bit to 23^(rd) bit of theinformation bit.

The DCI may include resource allocation of the PDSCH which is referredto as a downlink (DL) grant, resource allocation of a PUSCH which isreferred to as an uplink (UL) grant), a set of transmit power controlcommands for individual UEs in any UE group and/or activation of a voiceover Internet protocol (VoIP). The following Table 3 shows the DCI ofFormat 0 which includes uplink resource allocation information or anuplink grant.

TABLE 3 Carrier indicator—0 or 3 bits Flag for identifying Format0/Format 1A—1 bit, 0 indicates Format 0, 1 indicates Format 1A.Frequency hopping flag—1 bit, is a Most Significant Bit (MSB)corresponding to resource allocation at need and used to assign multipleclusters. Resource block assignment and hopping resource allocation—|log₂(N_(RB) ^(UL)(N_(RB) ^(UL) + 1)/ 2)|bits PUSCH hopping(corresponding to only single cluster assignment): N_(UL)_hop MSBs areused to obtain an n_(PRB)(i) value. (|log₂(N_(RB) ^(UL)(N_(RB) ^(UL) +1)/2)| − N_(UL)_hop) bits provide the resource allocation of the firstslot of an uplink subframe. In single cluster assignment, non-hoppingPUSCH (|log₂(N_(RB) ^(UL)(N_(RB) ^(UL) + 1)/2|) bits provide theresource allocation of an uplink subframe. In multi-cluster assignment,non-hopping PUSCH: Resource assignment is obtained from a combination ofa frequency hopping flag field and a resource block assignment andhopping resource allocation field. $\begin{matrix}{{\left\lceil {\log_{2}\left( \left( \frac{\left\lceil {{N_{RB}^{UL}/p} + 1} \right\rceil}{4} \right) \right)} \right\rceil\mspace{20mu}{bits}\mspace{14mu}{provide}\mspace{14mu}{resource}\mspace{20mu}{allocation}\mspace{20mu}{in}}\;} \\{{an}\mspace{14mu}{uplink}\mspace{14mu}{{subframe}.}}\end{matrix}\quad$ Wherein, P depends on the number of downlink resourceblocks. Modulation and coding scheme/redundancy version—5 bits New dataindicator—1 bit TPC command for a scheduled PUSCH—2 bits Cyclic shiftand OCC index for DM RS—3 bits Uplink index—2 bits, only exist for a TDDoperation, that is, an uplink-downlink configuration 0 DownlinkAssignment Index (DAI)—2 bits, only exist for TDD operations, that is,uplink-downlink configurations 1-6 CQI request—1 or 2 bits, a 2 bitfield is applied to a UE configured using at least one downlink cell.SRS request— 0 or 1 bit. Multi-cluster flag—1 bit.

Here, the flag is 1-bit information and is an indicator fordistinguishing the DCI 0 and the DCI 1A from each other. The hoppingflag is 1-bit information, and it indicates whether frequency hopping isapplied or not when a UE performs uplink transmission. For example, whenthe hopping flag is 1, it indicates that frequency hopping is applied atthe time of uplink transmission. When the hopping flag is 0, itindicates that frequency hopping is not applied at the time of uplinktransmission. The resource block assignment and hopping resourceallocation is also called a resource allocation field. The resourceallocation field indicates the physical locations and amount ofresources that are allocated to a UE. Although not shown in Table 3, anuplink grant includes redundant bits or padding bits for constantlymaintaining the total number of bits. The DCI has several formats.Although DCI has control information of a different format, the lengthof bits can be identically controlled using the redundant bits. Thus, aUE can perform blind decoding smoothly.

In Table 3, for example, if the resource allocation field has 13 bits ina band of an FDD 20 MHz, an uplink grant has a total of 27 bits except aCIF field and a CRC field. If the length of bits determined as the inputof blind decoding is 28 bits, an eNB makes the uplink grant the totalnumber of 28 bits by adding the redundant bits of 1 bit to the uplinkgrant at the time of scheduling. Herein, the all the redundant bits maybe set to 0 because they do not include special information. Of course,the number of redundant bits may be smaller than or greater than 2.

FIG. 6 is a view illustrating an example of a structure of an uplinksubframe carrying an ACK/NACK signal to which the present invention isapplied.

Referring to FIG. 6, an uplink subframe may be divided into a controlregion to which a physical uplink control channel (PUCCH) that carriesuplink control information is allocated; the control informationincludes an ACK/NACK response of downlink transmission. A data region towhich physical uplink shared channel (PUSCH) that carries user data isallocated in the frequency domain.

To maintain a single-carrier property, one UE may not simultaneouslytransmit the PUCCH and the PUSCH. However, if a UE is capable ofsimultaneous PUCCH/PUSCH transmissions, it is also feasible for one UEto transmit PUCCH and PUSCH at the same subframe. In the subframe, pairof RBs is allocated to the PUCCH with respect to one UE, and theallocated resource block (RB) pair is resource blocks corresponding todifferent subcarriers in each of two slots. This is called that the RBpair allocated to the PUCCH are frequency-hopped at a slot boundary.

The PUCCH may support multiple formats. Namely, it can transmit uplinkcontrol information having different number of bits per subframeaccording to a modulation scheme. PUCCH format 1 is used to transmit ascheduling request (SR), and PUCCH formats 1a and 1b are used totransmit an HARQ ACK/NACK signal. PUCCH format 2 is used to transmit aCQI, and PUCCH formats 2a and 2b are used to transmit a CQI and a HARQACK/NACK. When an HARQ ACK/NACK is transmitted alone, PUCCH formats 1aand 1b are used, and when an SR is transmitted alone, PUCCH format 1 isused. And PUCCH format 3 may be used for the TDD system, and also theFDD system. Meanwhile, as the increased demands for the high data ratetransmission, the mobile communication system composed of aggregatedmultiple CCs (component carriers) is being researched.

The ePDCCH can be one of solutions of limitation for a PDCCHtransmission or new control information transmission of near futurecommination system including a new type of carrier as shown in FIG. 7.The ePDCCH which can be multiplexed with the PDSCH can support multipleScells of the CA.

Referring to FIG. 7, the ePDCCH can be placed in data region whichconveys control information. So, the UE can monitor a plurality ofPDCCH/ePDCCHs within the control region and/or data region. As the PDCCHis transmitted on CCE, ePDCCH can be transmitted on eCCE (enhanced CCE)as an aggregation of some contiguous CCEs, the eCCE corresponds to aplurality of REGs. If ePDCCH is more efficient than PDCCH, it isworthwhile to have subframes where only ePDCCHs are used without PDCCHs.The PDCCHs and new ePDCCH only subframes, or have only ePDCCH onlysubframes can be in a new type of carrier as NC which has both legacyLTE subframes. It is still assumed that MBSFN subframes exist in a newcarrier NC. Whether to use PDCCH in MBSFN subframes in NC and how manyODFM symbols will be allocated if used can be configured via RRCsignaling. Further TM10 and new TM mode of UE can be considered for newcarrier type as well. Hereafter, new carrier type refers to a carrierwhere all or part of legacy signals can be omitted or transmitted indifferent manners. For example, a new carrier may refer a carrier whereCRS may be omitted in some subframes or PBCH may not be transmitted. Anew carrier may not mean that Rel-11 and below UEs may not be able toaccess the carrier. However, it is expected that Rel-11 and below UEsmay not achieve the same performance compared to legacy carrier due to acertain features lacking such as continuous CRS transmission.

As described, in the new carrier, a special subframe may not have legacyPDCCH and starts PDSCH at first OFDM symbol, the number of OFDM symbolsused in PDSCH in special subframe is increased to 8-11 from 7-10 innormal CP. When the number of OFDM symbols is equal to or greater than11 which is the basis of TBS calculation in normal subframe in normalcarrier, the scaling factor may be increased to 1. Furthermore, thisinvention proposes to use OFDM symbol 0, 1 for CSI-RS REs. The CSI-RScan be used for Radio Resource Management (RRM), fine time/frequencytracking and/or interference measurement. In small cell environmentswhere small cells are densely deployed, the CSI-RS in currentspecification may not be sufficient to perform those functions as thereare a large number of neighbor small cells which like to use orthogonalresources.

For this next LTE system or enhanced communication system, thisinvention provides that the new carrier cell may be introduced in whichall or some of the proposed backward compatible legacy signals and/orchannels are not transmitted for reasons of the improvement of aninterference problem between a plurality of cells, the enhancement ofcarrier extensibility, and an increase in the degree of freedom inproviding advanced features. Even though the proposed invention ismainly described for the new carrier cell as an example, it does notlimit to the new carrier cell only. It can be applied to legacy carrierswithout the loss of generality as well. More details, this inventionconsiders cases where cell-specific RS used for tracking and the RRMmeasurement would not be transmitted at all or transmitted only a subsetof subframes different from legacy carrier. For a convenience, thisinvention shows an example where CRS or tracking RS is transmitted every5 msec e.g., subframe #0 and #5 in each radio frame. More particularly,a new carrier may refer a carrier which performs cell on/off where eNBturns off transmissions upon no active UE attached or based on apattern. If this is assumed, this invention shows an example wherePSS/SSS/CRS or a discovery signal based on CSI-RS is transmitted every Tmsec with a predetermined value e.g., T=200, or more than 200. This canalso be applied to the macro cell with legacy carrier target in newcarrier's environment, or with the macro cell in small cells clusterenvironment.

As being different from a macro cell, typically, a small cell may nothave many attached UEs. In typical cases, there will be only a few or10-20 users per small cell. To mitigate inter-cell interference issueamong small cells, it is likely that enhanced PDCCH (ePDCCH) would beused in small cells rather than PDCCH. More specifically, it is expectedthat carrier used for small cell may not even carry PDCCH with veryminimal or non-cell specific RS. For this proposed embodiment supportsas a carrier without PDCCH yet scheduling PDSCH.

In current LTE specification, for a macro cell, a number of features aredesigned based on relatively large number of UEs. For example, controlsignaling design, PHICH, HARQ ACK mechanisms are designed for the casewhere a large number of UEs are multiplexed and serviced simultaneously.

When there are only a few UEs attached to a cell, some optimizations canbe considered. Another example is a cell specific feature such as CRS,SIB transmission, etc. If the arrival rate of a new UE is relativelylow, those cell specific features's overhead needs to be minimized. Toaddress the relatively low new UE arrival rate and minimize the cellspecific signaling, one easy approach to consider is ‘reactive’ approachwhere cell specific signaling is transmitted only upon the request.

For example, rather than depending on ‘proactive’ signaling of cellspecific feature, upon a request from a UE, signaling or information canbe given. A small cell may not carry periodic CRS nor SIB transmissionin this proposed embodiment.

To handle the legacy UE access, one approach which may not still supportfirst time visit UEs, is to use ‘proximity’ signal from a legacy UE asif it is approaching to CSG (Closed Subscriber Group). When a UE detectsnear-by small cell, it may initiate a proximity signal to the servingcell e.g., a macro cell which will then initiate cell specific featuresfor the UE. This approach becomes inefficient when the number of usersbecomes a bit large (e.g., 10-20) as it may require redundanttransmission of cell specific signaling/information for each UE.

At a certain threshold, a cell may determine that ‘proactive’ approachis better. If this occurs, a cell-broadcast signaling can be given to aUE to indicate that system information and CSS is enabled. Anotherexample is to control signaling such as PDCCH and/or ePDCCH. Inparticular, ePDCCH localized or distributed set does design may needfurther consideration of small number of UEs.

In current ePDCCH design, ePDCCH and PDSCH are not allowed to bemultiplexed in a PRB (Physical Resource Block) pair. For a localizedePDCCH set, if one PRB pair is configured for the localized ePDCCH set,up to 4eCCEs are available which can support up to 4 UEs withaggregation level (AL)=1. If interference is coordinated very well, in asmall cell environment, it may be expected that a UE may have high SNIRand thus AL is low. When a number of serving UEs is small, it may bepossible that there is less than 4 UEs per subframe scheduled by ePDCCHeven though all users are shared the same set of PRBs for ePDCCH sets.

This may become more serious problem with distributed ePDCCH set where 4PRB pairs or 8 PRB pairs are configured for one ePDCCH set. Thus, 16 or32 eCCEs are available per subframe which can hold up to maximium 16 or32 UEs.

To address this issue, before discussing the adaptation, it shows a fewcases per number of serving UEs. When the number of UEs is small around10-20, a control overhead shall be minimized. Multiple approaches inthis proposed embodiment can be considered.

Firstly, a PDSCH scheduling based on SPS configuration can be used.Instead of using dynamic DCI to schedule each PDSCH, the SPS schedulingmay be utilized.

Secondly, a system bandwidth where PDCCH is transmitted can be reduced.When the number of UEs is small, MIB may carry lower system bandwidththan actual system bandwidth so that legacy PDCCH does not consume toomany resources. For example, if there is only one UE served by PDCCH,system bandwidth can be advertised with 6PRB instead of 100PRB (actualsystem bandwidth) where PDCCH will be carried over 6PRB only. Other94PRBs can be used for data portion.

Thirdly, multiplexing ePDCCH and PDSCH can be used. For the same UE, ifconfigured by higher layer or indicated in DCI, multiplexing of ePDCCHand PDSCH is allowed within a PRB to reduce the waste. Or, if the cellstate is in low_active (i.e., the number of UE is small), UEs shallassume that ePDCCH and PDSCH multiplexing is allowed.

Fourthly, limitation for ePDCCH to first slot or second slot can be usedto reduce ePDCCH REs, the ePDCCH may be limited to only one slot in eachPRB pair.

Lastly, cross-subframe scheduling can be used. Multiple DCIs orcross-subframe scheduling DCIs can be scheduled in one subframe toschedule multiple subframes to maximize the utilization of configuredcontrol signaling portion e.g., one PRB pair configured for ePDCCH, oneOFDM symbol used for PDCCH.

Hereinafter, subframe bundling using ePDCCH monitoring subframeconfiguration is described. As another approach to reduce controloverhead and processing overhead when the number of UEs is small is touse subframe bundling where one DCI schedules PDSCH over multiplesubframes as shown in FIG. 8.

When a UE is configured with ePDCCH monitoring subframe set and the UEis supposed to monitor only ePDCCH in those configured subframes, the UEmay assume that in non-ePDCCH monitoring the PDSCH using the sameresource scheduled in previous ePDCCH can be continuously transmittedwithout scheduling DCI (in other words, PDCCH will not be present toschedule unicast data for that UE in other subframes, yet, PDCCH may bestill present to schedule cell-common data), if the non-ePDCCHmonitoring subframes are not MBSFN subframes with CRS-TM configured suchas TM4 or if a UE is configured with DM-RS based transmission mode suchas TM9/10. Depending on the ePDCCH set configuration, the number ofconsecutive (or non-consecutive due to intermediate MBSFN subframe withCRS-based TM configured) subframes scheduled by one ePDCCH. For theuplink transmission, the bundling window where the same PUSCH resourcecan be assumed can be signaled separately. Additionally, which subframescan be used for the same resource allocation and scheduling informationcan be signalled explicitly either via bitmap signaling or bundlingwindow or other means.

If there is no bundling window is configured for uplink, the UE shallassume only one subframe is scheduled by one uplink scheduling DCI.Similar to TTI bundling, HARQ-ACK timing is determined by the lastsubframe carrying PDSCH. Alternatively, a UE may be configured withsubframe bundling window for downlink PDSCH as well. If it isconfigured, a UE may assume that one downlink DCI is scheduling PDSCHover the bundling window using the same resource where it may assumethat except for the first subframe, ePDCCH is not transmitted in thebundling window. If there is MBSFN subframe within a bundled window, UEshall ignore that subframe from a bundling window if a UE is configuredwith CRS-based transmission mode and thus PDSCH will not be scheduled inthose MBSFN subframes. For DM-RS based TM case, a UE may assume thatMBSFN may not carry PDSCH and thus ignore MBSFN subframes from thebundling window otherwise it is configured to assume differently such asvia higher layer signaling of applicable subframe bitmap. In terms ofdeciding bundling window, two options are possible. One is determined bythe subframe index only so that MBSFN subframe will not be used forbundling unless configured otherwise and the other is determined by thenon-MBSFN subframes.

Control overhead adaptation can be done by reconfiguration of ePDCCHmonitoring subframes or bundling window size. Another simple approach isto configure a UE with bundling window size k which is used for bothdownlink and uplink. Once it is configured with a bundling window sizek, a UE can assume that only one (the first non-MBSFN subframe in thebundled subframes) subframe will carry ePDCCHs for the UE. Regarding therest of subframes, another higher layer signaling can be given todetermine the behavior among PDSCH or PUSCH continuation over thebundling subframes or, DTX/DRX.

Or, if bundling window is configured, cross-subframe or multi-subframescheduling DCIs can be placed in the first subframe for successivesubframes within the bundling window. It is also notable that DCI itself(first (E)PDCCH) can carry the number of applicable subframes similar tomulti-subframe scheduling.

To summarize the adaptive cell behavior, a carrier may do thefollowings. It transmits discovery signal only when inactive state or nouser is attached or the number of served UE is small. Discovery signalmay carry the information with ‘low UE level’ so that UEs can requestdelivery of system information and others when needed. A UE may performinitial RRM and cell discovery using discovery signal. Systeminformation can be delivered by USS upon request. Paging and othercell-specific information will be signaled to each UE via USS. Theuplink resource and timing to transmit ‘request’ to receive systeminformation, either prefixed resource/timing can be used or given by thecurrent serving cell or use RACH-like uplink signaling. Or, a new uplinkchannel can be defined which is used to indicate ‘proximity’ toneighboring small cells.

Upon reaching a threshold, a carrier may decide to change its mode to‘proactive’ mode where system information and cell-broadcast (e.g., CSS)can be enabled. This information is known to existing UEs via higherlayer signaling. Alternatively, a UE may perform blind decoding to findwhether CSS is enabled or not.

Once CSS is enabled, a UE can initiate BD on both USS (UE-specificsearch space) and CSS (common search space). The following table 4 showsavailable search space to UE.

TABLE 4 Number of Search Space Aggregation Size PDCCH DCI Type level L[in CCEs] candidates formats UE-specific 1 6 6 0, 1, 1A, 2 12 6 1B, 1D,2, 4 8 2 2A 8 16 2 Common 4 16 4 0, 1A, 1C, 8 16 2 3/3A

Moreover, when a carrier changes its mode to ‘proactive’ mode, it maychange its scheduling mechanism as well. The scheduling mechanism can behigher-layer signaled as well.

Depending on the number of UEs, a cell can take three states: dormant,low_active and high_active. In dormant, there is no UE connected to thecell. Low_active state can be used for a low number of UEs served andhigh_active can be used for the large number of UEs. In high_activestate, cell-specific signaling such as PSS/SSS and/or SIB and/or CRS canbe transmitted whereas in low_active state, those signals will betransmitted to each UE separately upon request.

FIG. 9 shows examples of dynamic cell configuration based on a cellstate which the present invention is applied.

Referring to FIG. 9, a macro cell checks how many UE is attached in asmall cell, the macro cell is an example as a control node, the macrocell can be a master cell (super cell) in small cell cluster, or a Pcellin CA environment, that is the macro cell includes any representativeprocessing node in dynamic cell environments. In other words, wheninactive state or no user is attached or the number of served UE is thesmall cell, the cell transmits a discovery signal only or UE specific RSsuch as PSS/SSS and/or SIB and/or CSS based on each UE separately sothat it leads to a minimized RS signals transmission.

This invention however is not restricted to the case where additionalcontrolling eNB is present. A eNB can make a decision based on thenumber of its associated UEs and other information to determine itsstate, and the cell state can be broadcasted either via MIB and/or SIBor cell-common broadcast dynamically or semi-statically. When a UE isreceived the cell state change, it can change its assumption onscheduling and cell-common control/data transmission. More specifically,the cell state can include also the cell on/off operation where when aeNB does not have many legacy UEs associated, it may perform dynamiccell on/off.

The macro cell checks whether a number of UEs in a small cell is lessthan or equal to a predetermined number of UEs (910). The number of UEsin a small cell is one of conditions to define a cell state, it is anelement to determine dynamic cell configuration according to a cellstate. The cell state includes a dormant mode, a low_active mode andhigh_active mode. Those of the dormant mode, the a low_active mode andthe high_active mode are classified based on a number of active UE in acell, data offloading, traffic pattern, or UE mobility. Herein that a UEmobility is low is considered as that the UE is attached to in a smallcell.

The macro cell or CN (or eNB) determines a cell state among the threestates based on one of conditions, the cell configuration can be changedby a cell state (920, 930). The cell configuration is preset accordingto the cell state separately. Or, the cell configuration is changed bydynamic DCI. That is, an indication for the cell state is followed assemi static configuration. Or, a cell off state is considered only whendiscovery signal is transmitted or less RS signals are transmitted, thecell can communicate the UE with applying RS resource and transmissionperiod (940). The cell state as a conservation mode includes the dormantor the low_active in which a resource for the reference signal issmaller than a resource for a high_active, and a transmission period ofthe reference signal when the cell state is in the dormant or thelow_active is longer than a transmission period of a reference signalwhen a cell state is in the high_active.

FIG. 10 shows examples of a flowchart of dynamic cell configuration bythe UE which the present invention is applied.

Referring to FIG. 10, the UE may receive a configuration includingsystem bandwidth by a serving cell (Scell) configuration, a transmissionmode (TM) configuration, or a radio resource control (RRC) configuration(1000). The UE can determine a cell state based on the configuration,the configuration is set based on a cell state that is determined by atleast one of a number of UEs, a data offloading, a traffic pattern, andUE's mobility by a macro cell or eNB (or CN). The macro cell can be amaster cell (super cell) in small cell cluster, or a Pcell in CAenvironment, which is the macro cell includes any representativeprocessing node in dynamic cell environments.

The UE receives a reference signal such as a discovery signal via thecell, the cell is a dormant or a low_active in which a resource for thereference signal is smaller than a resource for a high_active as normalcell, and a transmission period of the reference signal when the cellstate is in the dormant or the low_active is longer than a transmissionperiod of a reference signal when a cell state is in the high_active ofthe normal cell (1010). Herein the UE can also receive an indication toindicate a cell state (1005), the indication is signaled with a DCI, aMAC signal, or RRC signal so the UE can assume that the reference signalsuch as a discovery signal is less transmitted and save the resource forthe reference signal such as a discovery signal than a normaltransmission condition (1020). Wherein the cell state as a conservationmode includes the dormant or the low_active in which a resource for thereference signal is smaller than a resource for a high_active, and atransmission period of the reference signal when the cell state is inthe dormant or the low_active is longer than a transmission period of areference signal when a cell state is in the high_active.

Upon detecting a cell state change, a UE changes radio resourcemeasurement procedure accordingly. For example, if the cell statechanges from low_active to high_active, it may imply that CRS will bepresent in every subframe and thus measurement such as RRM (radioresource management) or RLM (radio link monitoring) can be performed perevery subframe and the threshold for each measurement can be adaptedaccordingly following either preconfigured threshold values or higherlayer configured values. If the cell state changes from high_active tolow_active or to dormant state, the measurement should be done insubframes where discovery signals are transmitted.

To support this, a UE can be configured with potentially multiplemeasurement objects in prior where each measurement object can be mappedto different cell state and the appropriate measurement object will betriggered (autonomously by the UE) upon detecting a cell state change.It will be applied also to CSI feedback where different restrictedmeasurement subframe sets can be configured and different configurationsare feasible. For a neighbor cell measurement, unless a UE knows thestate of neighbor cells, measurement would be done based on theassumption that the neighbor cell would be in dormant state. It ishowever possible that higher layer can configure the state of neighborcells such as by configuring measurement objects. When a UE performsmeasurement using cell-common RS such as CRS, depending on thecell-state, the set of subframes which carry cell-common RS will bechanged. One example of dormant state is that UE would not assume thatCRS will be present in any subframe or only in subframes carryingdiscovery signals if discovery signals include CRS. In low-active state,a UE can assume that subframe #0/#5 in every radio frame can carry CRSwhere the antenna ports are determined by reading PBCH or configured byhigher layer. In high-active, a UE can assume that all subframes carryCRS.

Thus, when it performs DRX or restricted measurement, the assumption onCRS-carrying subframes will be used appropriately. For example, radiolink monitoring requires to read CRS to emulate the quality of (E)PDCCH.Thus, RLM can be performed in a subframe carrying CRS. Since a UE needsto perform RLM at least once every DRX cycle, a UE may wake up alignedwith CRS-subframe at least once per every DRX to read CRS. Or, it cansimply assume that (E)PDCCH monitoring subframe will also carry CRS andthus a UE can wake up in one of those subframes to perform RLM as wellas monitoring (E)PDCCH during DRX operation. When a cell state is indormant state, a UE may not perform RLM due to the lack of CRSsubframes.

In summary, different cell state can be optimized differently in termsof resource management depending on the scenario. To reflect the dynamicsituation changes effectively, dynamic changes of cell state would besupported where cell-state change can be applied by the UE by changingthe configuration sets for radio resource and by changing UE measurementprocedures.

The UE can request system information including a paging and othercell-specific information based on the UE specific request (1030) andreceive the system information requested by using USS (1035). Asdescribed, the number of UE is small in a small cell and the UE each hasa low mobility in the cell so that the UEs can receive the signalincluding paging and cell-specific information during a UE-specificsearch space upon the request separately. This proposed embodimentfurther includes that system information is received upon the request ofa small group set, the small group set is categorized by the number ofUEs, a data offloading, a traffic pattern, and UE mobility. Thus, the UEcan receive system information including different paging andgroup-specific information in the cell based on the request of a smallgroup set. Also the dotted box as numbered 1005, 1030, 1035 can beomitted when it is defined to not necessary in UE side.

FIG. 11 is a block diagram showing a wireless communication systemaccording to an embodiment of the present invention.

A BS 1150 includes a processor 1151, a memory 1152, and a radiofrequency (RF) unit 1153. The memory 1152 is coupled to the processor1151, and stores a variety of information for driving the processor1151. The RF unit 1153 is coupled to the processor 1151, and transmitsand/or receives a radio signal. The processor 1151 implements theproposed functions, procedures, and/or methods. In the embodiments ofFIG. 2 to FIG. 10, the operation of the BS can be implemented by theprocessor 1151.

The processor 1151 configures an ePDCCH set to monitor in a predefinedsystem bandwidth, the ePDCCH set consists of PRBs for detecting apredetermined subframe(s) to indicate multiple subframes to scheduledata. The ePDCCH set is configured with a localized ePDCCH set or adistributed ePDCCH set. The processor 1151 makes to UE to receive theePDCCH monitoring subframe set to determine a resource for data, theePDCCH monitoring subframe set indicates a number of consecutivesubframes.

And the processor 1151 can configure MBSFN usage of the predefinedsystem bandwidth to supports MBMS services. Also, the processor 1151 canconfigure control information in a predetermined 6 Physical ResourceBlocks among a predefined system bandwidth including one of 1.4 MHz, 3MHz, 5 MHz, 10 MHz, and 20 MHz, or in a first slot or a second slot inone subframe. Or, the processor 1151 can control that the controlinformation at a predetermined subframe based on a cross-subframescheduling is signaled, and the data of PDSCH and the controlinformation of PDCCH or ePDCCH are multiplexed in PRBs to be defined bythe system bandwidth. Further the processor 1151 can Semi-PersistentScheduling (SPS) configuration to schedule data based on the cell state.

Especially, the processor 1151 can determine that the cell state is adormant, a low_active, or high active as normal condition, based on atleast one of a number of UEs, a data offloading, a traffic pattern, andUE mobility. When the processor 1151 can determine that the cell stateis a dormant or a low_active so that the processor 1151 can allocate aresource for the reference signal in the dormant or a low_active issmaller than a resource for a high_active, and control a transmissionperiod of the reference signal when the cell state is in the dormant orthe low_active is longer than a transmission period of a referencesignal when a cell state is in the high_active.

The wireless device 1160 includes a processor 1161, a memory 1162, andan RF unit 1163. The memory 1162 is coupled to the processor 1161, andstores a variety of information for driving the processor 1161. The RFunit 1163 is coupled to the processor 1161, and transmits and/orreceives a radio signal. The processor 1161 implements the proposedfunctions, procedures, and/or methods. In the embodiments of the FIG. 2to FIG. 10, the operation of the UE can be implemented by the processor1161.

Especially, the processor 1161 may configure one or more cells withdifferent frequencies, for this invention the processor 1161 configuresthe cells to support Semi-Persistent Scheduling, TTI-bundling, HARQ-ACKprocedures. The processor 1161 may receive, check and configureconfigurations for RS signals on a first cell as macro cell and a secondcell of small cell to support optimized RS transmission and resourceusage. The processor 1161 configures an ePDCCH set to monitor in apredefined system bandwidth, the ePDCCH set consists of PRBs fordetecting a predetermined subframe(s) to indicate multiple subframes toschedule data. The ePDCCH set is configured with a localized ePDCCH setor a distributed ePDCCH set. The processor 1161 checks to receive theePDCCH monitoring subframe set to determine a resource for data, theePDCCH monitoring subframe set indicates a number of consecutivesubframes.

And the processor 1161 can configure MBSFN usage of the predefinedsystem bandwidth to supports MBMS services. Also, the processor 1161 canconfigure control information in a predetermined 6 Physical ResourceBlocks among a predefined system bandwidth including one of 1.4 MHz, 3MHz, 5 MHz, 10 MHz, and 20 MHz, or in a first slot or a second slot inone subframe. Or, the processor 1161 can control that the controlinformation at a predetermined subframe based on a cross-subframescheduling is signaled, and the data of PDSCH and the controlinformation of PDCCH or ePDCCH are multiplexed in PRBs to be defined bythe system bandwidth. Further the processor 1161 can Semi-PersistentScheduling (SPS) configuration to schedule data based on the cell state.

Especially, the processor 1161 also receive a configuration includingsystem bandwidth by a serving cell (Scell) configuration, a transmissionmode (TM) configuration, or a radio resource control (RRC) configurationso that the UE can determine a cell state based on the configuration,the configuration is set based on a cell state that is determined by atleast one of a number of UEs, a data offloading, a traffic pattern, anda UE mobility by a macro cell or eNB (or CN).

The processor 1161 can also determine that the cell state is a dormant,a low_active, or high active as normal condition, based on allocation ofresource for the reference signal in the dormant or a low_active issmaller than a resource for a high_active, and control a transmissionperiod of the reference signal when the cell state is in the dormant orthe low_active is longer than a transmission period of a referencesignal when a cell state is in the high_active. To have systeminformation to the cell, the processor 1161 can request and receive asignal including paging and cell-specific information during aUE-specific search space upon the request. So this proposed embodimentshows a small cell in particular focused on adaptive cell behavior basedon the number of serving UEs. Thus, a cell specific RSs such as CRS,SIB, or paging and synchronization transmission as overhead in the cellcan be minimized based on the active UEs.

The processor may include application-specific integrated circuit(ASIC), other chipset, logic circuit and/or data processing device. Thememory may include read-only memory (ROM), random access memory (RAM),flash memory, memory card, storage medium and/or other storage device.The RF unit may include baseband circuitry to process radio frequencysignals. When the embodiments are implemented in software, thetechniques described herein can be implemented with modules (e.g.,procedures, functions, and so on) that perform the functions describedherein. The modules can be stored in memory and executed by processor.The memory can be implemented within the processor or external to theprocessor in which case those can be communicatively coupled to theprocessor via various means as is known in the art.

In the above exemplary systems, although the methods have been describedon the basis of the flowcharts using a series of the steps or blocks,the present invention is not limited to the sequence of the steps, andsome of the steps may be performed at different sequences from theremaining steps or may be performed simultaneously with the remainingsteps. Furthermore, those skilled in the art will understand that thesteps shown in the flowcharts are not exclusive and may include othersteps or one or more steps of the flowcharts may be deleted withoutaffecting the scope of the present invention.

The invention claimed is:
 1. A method for performing a cell management,performed by an user equipment (UE), the method comprising: receiving aradio resource configuration based on a cell state; detecting areference signal via the cell; determining the cell state by thereference signal; receiving a Semi-Persistent Scheduling (SPS)configuration to schedule data based on the cell state; and adapting aradio resource measurement based on the cell state.
 2. The method ofclaim 1, wherein the cell state includes a dormant or a low_active inwhich a resource for the reference signal is smaller than a resource fora high_active, and a transmission period of the reference signal whenthe cell state is in the dormant or the low_active is longer than atransmission period of a reference signal when a cell state is in thehigh_active.
 3. The method of claim 1, wherein the cell state isdetermined by at least one of a number of UEs, a data offloading, atraffic pattern, and a UE mobility.
 4. The method of claim 1, furthercomprising; receiving an indication whether the cell state is changedfrom a normal transmission state to a minimal transmission state for thereference signal when a number of UEs in the cell is smaller than orequal to a predetermined number of UEs; or requesting system informationto the cell and receiving a signal including paging and cell-specificinformation during a UE-specific search space upon the request.
 5. Themethod of claim 1, further comprising; detecting control information ina predetermined 6 Physical Resource Blocks among a predefined systembandwidth including one of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, and 20 MHz;detecting the control information in a first slot or a second slot inone subframe; or detecting the control information at a predeterminedsubframe based on a cross-subframe scheduling, the cross-subframescheduling indicates multiple subframes to schedule data.
 6. The methodof claim 1, further comprising; detecting data and the controlinformation in PRBs to be defined by the system bandwidth in the radioresource configuration, the data and the control information aremultiplexed.
 7. The method of claim 1, further comprising; receiving anenhanced Physical Downlink Control Channel (ePDCCH) monitoring subframeset to determine a resource for data, the ePDCCH monitoring subframe setindicates a number of consecutive subframes.
 8. A wireless device forperforming a cell management in a wireless communication system, thewireless device comprises: a radio frequency (RF) unit for transmittingand receiving a radio signal; and a processor that: controls the RF unitto receive a radio resource configuration based on a cell state; detectsa reference signal via the cell; determines the cell state by thereference signal; controls the RF unit to receive a Semi-PersistentScheduling (SPS) configuration to schedule data based on the cell state;and adapt a radio resource measurement based on the cell state.
 9. Thewireless device of claim 8, wherein the cell state includes a dormant ora low_active in which a resource for the reference signal is smallerthan a resource for a high_active, and a transmission period of thereference signal when the cell state is in the dormant or the low_activeis longer than a transmission period of a reference signal when a cellstate is in the high_active.
 10. The wireless device of claim 8, whereinthe cell state is determined by at least one of a number of UEs, a dataoffloading, a traffic pattern, and a UE mobility.
 11. The wirelessdevice of claim 10, wherein the processor further: detects controlinformation in a predetermined 6 Physical Resource Blocks among apredefined system bandwidth including one of 1.4 MHz, 3 MHz, 5 MHz, 10MHz, and 20 MHz; detects the control information in a first slot or asecond slot in one subframe; detects the control information at apredetermined subframe based on a cross-subframe scheduling, thecross-subframe scheduling indicates multiple subframes to schedule data;or detects data and the control information in PRBs to be defined by thesystem bandwidth in the radio resource configuration, the data and thecontrol information are multiplexed.
 12. The wireless device of claim 8,wherein the processor further: controls the RF unit to receive anindication whether the cell state is changed from a normal transmissionstate to a minimal transmission state for the reference signal when anumber of UEs in the cell is smaller than or equal to a predeterminednumber of UEs; or requests system information to the cell and receivinga signal including paging and cell-specific information during aUE-specific search space upon the request.
 13. The wireless device ofclaim 10, wherein the processor further: controls the RF unit to receivean enhanced Physical Downlink Control Channel (ePDCCH) monitoringsubframe set to determine a resource for data, the ePDCCH monitoringsubframe set indicates a number of consecutive subframes.